TTAllpass2c.h

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/** @file
 *
 * @ingroup dspFilterLib
 *
 * @brief #TTAllpass2c is a second-order building-block allpass filter.
 *
 * @details Essentially the same as #TTAllpass2a, but with some signs flipped.
 *  Based on Fredric J. Harris (2004): Multirate Signal Processing for Communication Systems, Prentice Hall, Chapter 10, Figure 43. @n
 *  @n
 *  Difference equation: @n
 *  @code
 *  y(n) = -e_2 x(n) - e_1 x(n-1) - x(n-2  -  e_1 y(n-1) - e_2 y(n-2)
 *  @endcode
 *
 *  Transfer function: @n
 *
 *  @code
 *           -e_2  -  e_1 Z^(-1)  -  Z^(-2)
 *  H(Z) = ---------------------------------
 *          1  +  e_1 Z^(-1)  +  e_2 Z^(-2)
 *  @endcode
 *
 * @authors Timothy Place, Trond Lossius
 *
 * @copyright Copyright © 2010, Timothy Place @n
 * This code is licensed under the terms of the "New BSD License" @n
 * http://creativecommons.org/licenses/BSD/
 */


#ifndef __TT_ALLPASS2C_H__
#define __TT_ALLPASS2C_H__

#include "TTDSP.h"


/** A second-order building-block allpass filter.
    Essentially the same as TTAllpass2a, but with some signs flipped.
    Based on Multirate Signal Processing for Communication Systems, Chapter 10, Figure 43. 
 
    difference equation:
        y(n) = -e_2 x(n) - e_1 x(n-1) - x(n-2  -  e_1 y(n-1) - e_2 y(n-2)

    transfer function:
                -e_2  -  e_1 Z^(-1)  -  Z^(-2)
        H(Z) = ---------------------------------
                1  +  e_1 Z^(-1)  +  e_2 Z^(-2)
 */
class TTAllpass2c : public TTAudioObjectBase {
    TTCLASS_SETUP(TTAllpass2c)
    
protected:
    
    TTFloat64           mE1;    ///< first coefficient
    TTFloat64           mE2;    ///< second coefficient
    
    TTSampleVector      mX1;    ///< previous input sample (n-1) for each channel
    TTSampleVector      mX2;    ///< previous input sample (n-2) for each channel
    TTSampleVector      mY1;    ///< previous output sample (n-1) for each channel
    TTSampleVector      mY2;    ///< previous output sample (n-2) for each channel
    
    // Notifications
    TTErr updateMaxNumChannels(const TTValue& oldMaxNumChannels, TTValue&);
    
    // Zero filter history
    TTErr clear();
    
    // Do the processing
    TTErr processAudio(TTAudioSignalArrayPtr inputs, TTAudioSignalArrayPtr outputs);
    
    /** Unit Tests
     @param returnedTestInfo        Used to return test information
     @return                        #TTErr error code if the method fails to execute, else #kTTErrNone.
     */
    virtual TTErr test(TTValue& returnedTestInfo);
    
public:
    TTErr calculateValue(const TTFloat64& x, TTFloat64& y, TTPtrSizedInt channel=0);
};


#endif // __TT_ALLPASS2A_H__